Fundamentally, the recording of topographic scans with the aid of computed tomography scanners has been known for a long time. For example, published Specification DE 26 13 809 describes a method for production of transverse layer images with the aid of a tube detector unit, with the detector having a large number of individual detectors and the tube detector combination being shifted with a linear movement relative to the patient in order to produce the transverse layer images, and with a transverse layer image or else topographic scan being obtained from the measured data obtained during the relative movement of the tube detector combination with respect to the patient.
Patent Specification DE 41 03 588 C1 describes a computed tomography scanner which has a rotating tube detector combination which on the one hand rotates about the central axis, and is at the same time shifted relative to the patient in the direction of the central axis. This is done in order to scan a patient. The scanning data from specific projection directions is used in order once again to create a topographic scan by composition of the measured data from these specific projection directions. The radiation load on the patient is, of course, relatively high during a measurement such as this since the patient is also subjected to a dosage load at projection angles which are not required for the topographic scan.
Laid-Open Specification DE 199 61 524 A1 also discloses a scanning method such as this with a computed tomography scanner for a patient. A topographic scan is also determined in this case during a spiral scan by adding up the measured data at the detector system for specific projection angles from the measured data determined during the spiral scan so that this data is combined to form a topographic scan or X-ray shadow image. This is done in order to make it possible to use this to determine the position and/or orientation of specific areas which are intended to be examined in more detail.
Furthermore, Laid-Open Specification DE 198 02 405 A1 also discloses a combination of a CT with a tube matrix detector combination and with an X-ray having a tube solid-state image converter combination. These are arranged at an angle of 90° to one another on a rotating rim. This appliance produces CT section images and X-ray shadow images at the same time, with the total dose that is applied in this case also being relatively high. Furthermore, only shadow images on one plane can be created in one operation.
While only topographic scans are produced in each of the documents cited above, in order to determine the position and/or orientation of regions of interest on a plane, the Laid-Open Specification DE 195 32 535 A1 mentions that the three-dimensional position and/or orientation of structures of interest can also be obtained by producing two orthogonal views or topographic scans. In order to produce these two topographic scans at an angle to one another as required for this purpose, a single-tube computed tomography scanner is used which either produces the two topographic scans that are required by linear scanning twice from different projection angles, or the measured values during a spiral scan are added up at at least two projection angles, thus resulting in the appropriate topographic scans.
The knowledge of the three-dimensional structure, for example the position, orientation and extent of the patient or the knowledge of the position, orientation and extent of a tumor in a patient is used either for dosage modulation for a subsequent CT scan or for radiation therapy planning in a radiation therapy appliance. With regard to dosage modulation, reference should be made, for example, to Laid-Open Specification DE 199 33 537 A1 or to the already cited Laid-Open Specification DE 195 32 535 A1.